The present invention relates to conveyors and, more particularly, to an intermediate drive and related method for driving at least one, and preferably a plurality of modular link conveyor belts forming part of a conveyor system.
Conventional conveyor systems employing endless belts are typically driven at one by a drive sprocket coupled to a rotating shaft. At the opposite end, an idler sprocket coupled to an idler shaft provides the necessary support function. Together, the drive and idler sprockets support the belt as it traverses along a corresponding guide rail or like structure to convey or move articles from one location to another.
While this arrangement is acceptable for most uses, driving or assisting the driving of a belt using an intermediate drive is desirable in some situations. One example of an intermediate drive for a xe2x80x9choldingxe2x80x9d conveyor system is disclosed in U.S. Pat. No. 4,142,625 to Bourgeois. In this conveyor system, a pair of parallel belts having longitudinally extending drive chain portions include rollers for rolling along a flat support table. One belt is driven over a first sprocket coupled to an intermediate drive shaft, while the other is trained under a spaced second sprocket carried on the same shaft. As a result of this xe2x80x9cover/underxe2x80x9d arrangement, the parallel belts are simultaneously driven in opposite directions when the single shaft supporting both spaced drive sprockets is rotated.
While this intermediate drive arrangement may be suitable for its intended purpose, several limitations remain. The first and perhaps most obvious limitation is that a catenary is formed in each just upstream and just downstream of each drive sprocket. Catenaries are generally undesirable, since they increase the incidence with which objects may become trapped between the conveyor belt and the sprocket. An object trapped in this position may create a deleterious jam, which in turn results in corresponding system downtime until appropriate corrective action is taken. Also, even a single catenary generally prevents the conveyor system from being turned on its side or inverted during operation.
Another shortcoming is that the ""625 patent does not suggest using the intermediate drive unit in conjunction with a conventional end drive unit. In particularly long sections of a conveyor, the weight of the corresponding endless belt and the concomitant increase in frictional resistance creates considerable stress and wear on both the sprocket and the links or other modular structures forming the belt. Of course, this increased wear is deleterious, since it reduces the service life of the main components in the conveyor system, which in turn increases the frequency with which maintenance is required.
In an effort to address and overcome these problems, U.S. Pat. No. 5,303,817 to Kissee discloses an intermediate drive assist for driving particularly long sections of a modular link conveyor belt. The drive assist employs a second, separately driven conveyor belt for simultaneously engaging and driving both the forward and return runs of the particular belt section. Each link forming the belt used in the assist includes a projection that interleaves in a corresponding recess in a link on the belt section. This is supposed to create an efficient force-transmitting engagement.
While this intermediate drive assist may generally enhance performance as compared to using an end drive alone, the improvement comes at a cost. Although the loading on the individual links may be reduced, the overall wear profile is increased, since the underside surfaces of the belt are engaged along both the forward and return runs. Requiring a second belt that must be tensioned and maintained throughout its life to ensure proper operation is also problematic. If the belt tension and wear is not kept in check, slipping may occur, which of course reduces efficiency and otherwise deleteriously effects the overall performance of the conveyor system.
Thus, a need is identified for an improved intermediate drive arrangement for driving at least one, and preferably a plurality of conveyor belts forming part of an overall conveyor system. In particular, the need for a catenary in a belt driven by an intermediate drive would be eliminated, which would not only improve performance, but also would reduce the incidence of deleterious jams. Wear could be reduced by providing an intermediate drive arrangement that engages the conveyor belt along only one of the runs, and most preferably, the return run. Also, the conveyor system with the intermediate drive should be capable of operating in any orientation, including even upside-down, without experiencing any reduction in efficiency or increase in wear. By addressing these needs, the end result would be a conveyor system having an intermediate drive that is an improvement over prior art proposals, especially in terms of operational flexibility and reliability.
In accordance with a first aspect of the invention, a conveyor system is disclosed comprising at least one conveyor belt formed of a plurality of modular links having at least one pair of guide tabs. At least one guide rail is provided for guiding the conveyor belt. The guide rail has upper and lower guide tracks for engaging the guide tabs of the links and guiding the conveyor belt along a forward and a return run, respectively. The guide rail also has a recessed portion along which the conveyor belt is guided. A drive for the belt includes at least one sprocket juxtaposed to the recessed portion of the guide rail. This sprocket engages the conveyor belt to drive it along the guide rail.
In the most preferred embodiment, the recessed portion of the guide rail adjacent to the drive is contoured or curved to correspond in shape to a peripheral surface of the sprocket. This allows for placement of the sprocket in juxtaposition to the belt. The modular links may further include a depending arm for carrying each guide tab, which is preferably an inwardly projecting transverse tab for engaging the guide tracks of the guide rail along the forward and return runs, respectively. The links may further include an apex and a pair of legs, with the apex including a slot for receiving a transverse member extending through an aperture in each leg of an adjacent link. As a result of this arrangement, the conveyor belt is capable of expanding and contracting in a longitudinal dimension.
The drive preferably includes a shaft for carrying the sprocket, along with first and second supports for supporting the shaft. The supports may be in the form of plates, each having an aperture for receiving the shaft. The support plates may be carried on either side of a single guide rail. A bushing may be positioned in the aperture in each support plate to create a low friction bearing surface for the shaft. A motive device is also provided for rotating the shaft, which in turn rotates the sprocket and drives the belt.
In one embodiment, a plurality of guide rails are provided for guiding a plurality of conveyor belts. Accordingly, the drive includes a plurality of sprockets mounted on a common shaft, each for driving at least one of the conveyor belts. Preferably, each of the plurality of guide rails is an I-beam guide rail. Like in the singular embodiment, the shaft is supported by first and second supports, but each support is carried by at least one of the plurality of guide rails (and most preferably, the first-in-line and last-in-line guide rails). Spacers may also be provided for spacing each shaft support from the adjacent guide rail, or the adjacent pairs of guide rails from each other.
In accordance with a second aspect of the present invention, a drive for a conveyor system having a plurality of conveyor belts, each driven along a separate guide rail having a recessed portion, is disclosed. The drive comprises at least one drive sprocket for engaging and driving each of the conveyor belts in the same direction. A shaft supports the drive sprockets, and first and second supports in turn provide support for the shaft. Each support is preferably carried by one of the plurality of guide rails, such that the shaft is supported and each sprocket is positioned in juxtaposition to the recessed portion of each separate guide rail for driving the corresponding conveyor belt.
Each conveyor belt is formed of a plurality of modular links, and each sprocket includes a plurality of teeth adapted for engaging and driving the links. Each sprocket may be a split sprocket including first and second halves held together by at least one fastener. The first and second supports may take the form of plates, each having an aperture for receiving the shaft. A bushing may be provided in each aperture to create a bearing surface for the shaft. At least one spacer is provided for spacing the first and second supports from the corresponding guide rail, as well as for spacing adjacent pairs of guide rails from each other. Each spacer may have recessed end potions that correspond in size and shape to locator holes formed in the guide rails and supports.
In accordance with a third aspect of the present invention, a method for driving a plurality of conveyor belts along a plurality of separate guide rails, each having a recessed portion, is disclosed. The method comprises providing a conveyor belt including a plurality of modular links having guide tabs for engaging each guide rail, positioning a drive including a plurality of sprockets such that each sprocket is juxtaposed to and at least in partial engagement with the conveyor belt along the recessed portion of each separate guide rail, and rotating the drive sprocket to simultaneously drive the plurality of conveyor belts in the same direction along the corresponding guide rails. In the preferred embodiment, each guide rail is an I-beam guide rail having forward and return runs, and the step of positioning the drive unit juxtaposed to the guide rail includes suspending first and second support plates from at least a two of the plurality of guide rails. Each support plate includes an aperture for receiving a shaft carrying the plurality of sprockets.
In accordance with a fourth aspect of the invention, a conveyor system is disclosed comprising a plurality of conveyor belts, each including a plurality of modular links; a guide rail corresponding to and guiding each conveyor belt, each guide rail having a contoured recessed portion along which said conveyor belt is guided; and a drive including a plurality of sprockets, each having a different diameter, and each juxtaposed to the recessed portion of the guide rail for engaging and driving the conveyor belt. The contour of the recessed portion on each guide rail corresponds to the diameter of the corresponding sprocket such that the proper engagement is maintained with the sprocket.
The drive may be positioned along a curve in the conveyor system, and the sprockets are coaxially mounted, gang-driven and sized to ensure that an outermost conveyor belt is driven at a higher rate of speed than an inner conveyor belt along the curve. Accordingly, an article being carried on the belts is kept at a desired orientation as the curve is traversed. To achieve this result in one embodiment, the sprocket for engaging an innermost conveyor belt has a smaller diameter and a fewer number of teeth than the sprocket for engaging the outermost conveyor belt in the curve.
In accordance with a fifth aspect of the present invention, a drive for use in a curved section of a conveyor system having a plurality of conveyor belts, with each belt being associated with a separate guide rail having a recessed portion with a different contour, is disclosed. The drive comprises a plurality of coaxially mounted drive sprockets having different diameters corresponding to a relative position of the adjacent conveyor belt along a radius of the curve. Each sprocket is held on a shaft in juxtaposition to the contoured recessed portion of the guide rail for engaging and driving each conveyor belt at a different speed.